If you quick save before identifying an item or opening a chest (before running you mouse over it or hitting alt), you can quick load to get different stats. Don't waste too much time doing this, though, since the game gets easier as it progresses and you don't really need the absolute best of everything. Starting a new game, I would set a low limit for reloading on major pieces of equipment (dragon armour set, etc) to make sure I didn't get something crappy, but that's about it.
I started to collect charms to use later, but the game becomes easier as it progresses, so I only used one. If you do not need to increase a stat or resistance, don't; that way if you do run into problems, you will have some open slots. Also, gold charms become much more common at the end of the game; before that the best you buy are silver (though you can find a few gold charms in the Dark Forest). Keep a few skill points in reserve, but don't max Enchant Weapon until you require it.
Mage spell books can be bought, so you don't necessarily have to put many skill points into them. With mana bonuses on equipment (maybe also from charms) and a few
restoration potions you can make an effective magic user from a warrior. The only real benefit a mage has over a warrior is receiving more mana per intelligence point.
Free skills, and spell books you can buy (Spoilers)